AN INVESTIGATION OF THE APPEARANCE OF POSITIVE MAGNETIC-MOMENTS ON FIELD COOLING SOME SUPERCONDUCTORS

Paramagnetic moments from some high-T(c) superconductors, measured using a SQUID magnetometer, are presented. Similar results have been published elsewhere (W.M. Lee et al., Solid State Commun. 74 (1990) 97.) with attempts to explain them in terms of a material property. We have investigated this phenomenon thoroughly and we show here adequate evidence that these moments are an artifice, a combination of peculiar circumstances in the machine. They arise largely through the flux trapping capabilities of the material and the inhomogeneity of the magnet in the machine. They can be explained using the known behaviour of materials containing trapped flux. They are not due to the remanent field of the magnet.